Isa Saharkhiz and his son Mehdi have n't seen each other in nearly a decade .

But the dream of a reunion between the dissident journalist and his 32-year-old son came one step closer to fruition when Iranian authorities unexpectedly released the elder Saharkhiz last week after imprisoning him for more than four years .

`` Yes , it was a surprise , '' said Saharkhiz , speaking by phone to CNN from his home in Tehran .

The longtime critic of the Iranian regime described how last Thursday , a prison official made an unannounced visit to the hospital room where he had been detained for months due to his deteriorating health conditions .

`` He told me that ` you are released now , ' '' Saharkhiz said . Within hours , he was back at his home surrounded by his wife and daughter and friends .

Mehdi was at the design company in northern New Jersey where he works as a production manager when his relatives in Iran called with news of his father 's release .

`` I was really shocked , '' he recalled .

Father was rounded up during 2009 unrest in Iran

Since 2009 , the younger Saharkhiz has led a one-man digital campaign from his home in New Jersey aimed at liberating his father .

`` I confess that I am not ashamed that my father is in prison . And I am proud of him ... his bravery has made life harder for the cowards in power , '' Mehdi announced on camera in Farsi , in a 2009 video he posted on YouTube .

The young man appeared in the video wearing a T-shirt printed with his father 's portrait .

Iranian security forces first arrested Isa Saharkhiz , 59 , during the summer of 2009 .

The former journalist had been working as an international spokesman for the campaign of Mehdi Karroubi , a moderate politician who ran for president in June 2009 .

Huge street protests erupted that month after Iranian authorities declared the firebrand incumbent candidate Mahmoud Ahmadinejad winner of the election . Opposition groups accused the Iranian regime of rigging the results in favor of Ahmadinejad , a claim Tehran vehemently rejected .

In the ensuing crackdown on what became known as the Green Movement , Karroubi and another opposition presidential candidate , Mir-Hossein Mousavi , were placed under house arrest .

Security forces used brute force and widespread arrests to crush the street protests , while also rounding up top officials from Mousavi and Karroubi 's political campaigns , including Isa Saharkhiz .

`` They tortured me , '' he said , describing how officers beat him and broke his ribs during his initial detention .

Iranian authorities justified the 2009 crackdown by frequently accusing opposition leaders of being part of a foreign conspiracy aimed at overthrowing the government . Iranian officials also accused some protesters of being mohareb , or enemies of God .

Chinese journalist Shi Tao released after 8 years in prison

Saharkhiz later received a sentence of three years in prison for conspiring against the government and insulting the Supreme Leader , Ayatollah Ali Khamenei .

Singled out as a former insider ?

During his incarceration , the writer said he was subjected to physical and emotional abuse , while also being held in solitary confinement for long periods .

`` In January , in the winter , they sent me on the roof of the jail for two hours when the weather was very cold , '' Saharkhiz said . `` They put me out without any shoes , any socks , and very few clothes . ''

Experts say Iranian authorities reserved especially harsh treatment of well-known intellectuals such as Saharkhiz because he was a former regime insider , who had risen to prominence after the Islamic Revolution of 1979 . For a decade , he worked as a reporter for one of the main state news agencies . He also founded a free-speech advocacy group called the Society for the Defense of Freedom on the Press .

`` Saharkhiz is not an outsider to the regime . Like others in the reformist movement that emerged from within the ranks of the government of the Islamic Republic , Saharkhiz angered many , including the Supreme Leader , '' said Behzad Yaghmaian , an Iranian-American academic and author of `` Social Change in Iran . ''

Yaghmaian commended Saharkhiz for his `` principled resistance to the government and the supreme leader . ''

`` People like Saharkhiz are considered even more dangerous than those opposing the regime from outside , '' he added .

As the elder Saharkhiz languished in prison in 2009 , his son Mehdi became an opposition activist from the relative safety of exile in New Jersey .

Using Twitter , Facebook and YouTube , Mehdi distributed amateur videos smuggled from Iran showing Iranian security forces beating and arresting demonstrators .

`` The least I can do is get their voices out , '' he said , in a 2010 interview with CNN .

Election of Rouhani may have had impact

Mehdi has lived in the United States for many years , and last year became a naturalized American citizen . His father was stationed in New York for several years in the 1990s while working for IRNA , the official Iranian news agency . During that time , Mehdi attended high school in suburbs outside New York City .

Four years after his arrest , the elder Saharkhiz said there was no formal reason given for his release . But he said the move was likely linked to the recent election of Hassan Rouhani to the post of president .

Several other dissidents detained during the 2009 crackdown were released last month , according to the English-language daily Tehran Times . The Iranian government never issued a formal explanation for why these political prisoners were freed .

Rouhani campaigned on a platform of reform and an end to Iran 's international isolation . Last month , he called for a negotiated end to Tehran 's long feud with Washington over its nuclear program . His charm offensive during a visit to the United Nations General Assembly climaxed with a brief phone conversation with Barak Obama . It was the first direct contact between American and Iranian presidents in more than 30 years .

`` Not the system , but the situation has changed , '' explained Isa Saharkhiz , during his interview with CNN .

Though optimistic about Rouhani 's presidency , Saharkhiz warned that Iran was a `` double state , '' where true power lies in the hands of Supreme Leader Khamenei and senior military commanders .

He argued that expanded relations with Washington and the removal of crippling economic sanctions would help moderate figures such as Rouhani engaged in policy and power struggles with Iranian hard-liners . Removal of American embargoes would also help ordinary Iranians who could no longer afford life-saving foreign phamaceuticals , he said .

Saharkhiz 's note of cautious optimism was echoed by his son .

`` There 's a lot of hope from what Rouhani did in the U.S. and there 's a lot of good response from the people , '' Mehdi said . `` But then you have a lot of people who were in charge before the election and are still in charge and do n't like it . ''

Son not sure when he can travel to Tehran

For now , Mehdi says it is not safe for him to return to Iran to visit his father . He has yet to fulfill his mandatory Iranian military service , and he fears he could be detained due to his own outspoken criticism of the regime .

`` Maybe in a few years I will be able to go back , but it 's a really big risk , '' he said .

Meanwhile , his father predicted he is still at risk of being thrown back in prison .

`` I will support freedom in Iran , and maybe criticize the leadership in Iran , '' he said . `` So it is possible that they will come here and capture me again . ''

Both father and son hope , however , that the authorities will lift an earlier travel ban that prevented the veteran journalist from leaving Iran .

If so , the two hope to reunite for the first time in more than a decade in a third country such as the United Arab Emirates or Turkey .

`` It will be a very emotional time , '' Isa Saharkhiz said .

It would be , his son said , a dream come true .

In April : Four Italian journalists released from captivity in Syria

@highlight

Dissident journalist recently released from prison

@highlight

Isa Saharkhiz had criticized country 's supreme leader

@highlight

His son , Mehdi , lobbied for his release from the U.S.